My tech skills are rusting horribly but I tried to briefly take a look at this…
I’m seeing the same behavior with the Firefox save-as file extension being .m4a vs the displayed URL showing .mp3.
Opening either extension in VLC and viewing the codec info (Tools->Codec Info / Ctrl+J) shows the actual encoding to be ‘MPEG AAC Audio (mp4a)’.
I didn’t try grabbing a file from the torrent, but if I use the media tab in Firefox ‘Page Info’ (Ctrl+I) to “save as” the embedded IA player file it suggests a matching .mp3 extension with the displayed address (but the codec is still mp4a).
The main thing I’m not following is what you mean by having parse errors in Mp3tag. So far I haven’t seen any metadata included in either the .mp3 or .m4a downloads (I only tested the first file), they both play audio fine, and if I browse to their directory in Mp3tag (vers. 2.57) it doesn’t seem to show anything unusual to me (empty metadata, no error/alert messages). What exactly is the parse error or how is it behaving differently from what’s expected?
I also just wanted to say “THANK YOU!” for an awesome support post. You posted it to the right community, gave it a short but very descriptive title, gave lots of info about what you’ve tried and the results you’ve experienced – and did so politely :)